Let me first say that I no longer pull doubles (truck, FW, utility trailer) because it was just to much of a hassle.
I was never pulled over but was approached twice by a CA DOT officer while we were stopped for the night. I wasn't over length so no issues. The second time the LEO said that he would use surroundings to judge length. Example if you are near a 53' commercial semi and look longer you are probable over 65'.
Many states will allow you to pass through as long as you are legal in the state you are registered. In Oregon we had the opportunity to talk with a state trooper and while we were apparently illegal in Oregon the fact that we were legal in CA (all were registered in CA) his head office instructed him too not write us up.
In all the miles we pulled doubles we drove safe, within speed limits and were in compliance with CA regulations and never had a problem. Every time we were approached we were stopped for the night or having lunch.